1. Field of the Invention
The present invention relates to an optical apparatus, such as a lens barrel, adapted for an image pickup apparatus, such as a video camera or the like.
2. Description of Related Art
Known zoom lenses for video cameras include such a zoom lens that is composed of four lens units including, for example, a fixed convex lens unit (having a positive refractive power), a movable concave lens unit (having a negative refractive power), a fixed convex lens unit (having a positive refractive power) and a movable convex lens unit (having a positive refractive power) arranged in this order from the side of an object of shooting.
FIGS. 6(a) and 6(b) show a popular lens barrel arrangement of a zoom lens of the above-stated four-lens-unit structure. FIG. 6(a) is a sectional view taken on a line Axe2x80x94A in FIG. 6(a).
Referring to FIGS. 6(a) and 6(b), the zoom lens is composed of four lens units, i.e., a front lens unit 201a arranged to be stationary, a variator lens unit 201b arranged to perform a magnification varying action by moving in the direction of an optical axis 205, an afocal lens unit 201c arranged to be stationary, and a focusing lens unit 201d arranged to keep a focal plane unvaried by the variation of magnification as well as to adjust focus by moving in the direction of the optical axis 205.
Guide bars 203, 204a and 204b are arranged in parallel with the optical axis 205 to guide and restrain the moving lens units from turning. A DC motor 206 is a drive source arranged to drive and move the variator lens unit 201b. 
The front lens unit 201a is held by a front lens tube 202. The variator lens unit 201b is held by a V moving ring 211. The afocal lens unit 201c is held by an intermediate frame 215, and the focusing lens unit 201d is held by an RR moving ring 214.
The front lens tube 202 is positioned on and secured to a rear tube 216. By using these two tubes 202 and 216, the guide bar 203 is positioned and held by them while a guide screw shaft 208 is rotatably supported by these tubes 202 and 216. The guide screw shaft 208 is arranged to be driven to rotate with the rotation of the output shaft 206a of the DC motor 206 transmitted through a gear train 207.
The V moving ring 211 which holds the variator lens unit 201b is provided with a ball 210, which engages a pressing spring 209 and is caused by the force of the pressing spring 209 to engage a screw groove 208a formed in the guide screw shaft 208. The V moving ring 211 is thus arranged to move back and forth in the direction of the optical axis 205 while being guided and restricted from turning by the guide bar 203 when the guide screw shaft 208 is driven to rotate by the DC motor 206.
The guide bars 204a and 204b are fitted into and supported by the rear tube 216 and the intermediate frame 215 which is positioned on the rear tube 216. The RR moving ring 214 is arranged to be movable back and forth in the direction of the optical axis 250 while being guided and restrained from turning by the guide bars 204a and 204b. 
The RR moving ring 214, which holds the focusing lens unit 201d, has sleeve parts into which the guide bars 204a and 204b are slidably fitted. A rack 213 is mounted on the RR moving ring 214 and is arranged to be integral with the RR moving ring 214 in the direction of the optical axis 250.
A stepping motor 212 is arranged to drive and rotate a lead screw 212a formed integrally with the output shaft thereof. The lead screw 212a engages the rack 213 which is mounted on the RR moving ring 214. When the lead screw 212a rotates, the RR moving ring 214 moves in the direction of the optical axis 250 while being guided by the guide bars 204a and 204b. 
As for a drive source to be used for the variator lens unit 201b, a stepping motor may be used similarly to the drive source for the focusing lens unit 201d. 
A lens barrel body in which the lens units, etc., are housed in an approximately sealed state is formed by the front lens tube 202, the intermediate frame 215 and the rear tube 216.
In a case where the lens unit holding frames are arranged to be moved by means of stepping motors, the absolute position of each holding frame is detected by counting driving pulses applied to the stepping motor after the holding frame is detected to be at a reference position in the direction of the optical axis by means of a photo-interrupter or the like.
FIG. 7 shows the electrical arrangement of a camera body in a conventional image pickup apparatus. In FIG. 7, the components of the lens barrel described above with reference to FIGS. 6(a) and 6(a) are indicated by the same reference numerals as those used in FIGS. 6(a) and 6(a).
Referring to FIG. 7, a solid-state image sensor 221 is composed of a CCD or the like. A zoom driving mechanism 222 is arranged to drive the variator lens unit 201b and includes the motor (or a stepping motor) 206, the gear train 207 and the guide screw shaft 208, etc.
A focusing driving mechanism 223 is arranged to drive the focusing lens unit 201d and includes the stepping motor 212, the lead screw 212a, the rack 213, etc.
An iris driving mechanism 224 is arranged to drive an iris device 235 which is disposed between the variator lens unit 201b and the afocal lens unit 201c. 
A zoom encoder 225 and a focus encoder 227 are arranged to detect the absolute positions of the variator lens unit 201b and the focusing lens unit 201d, respectively, in the direction of the optical axis. In a case where a DC motor is employed as a variator drive source as in the case of FIGS. 6(a) and 6(a), a potentiometer or a magnetic encoder is employed as the absolute position encoder. If a stepping motor is employed as the drive source, it is generally practiced to set the holding frame at a reference position and, after that, to continuously count the number of operation pulses applied to the stepping motor as mentioned above.
An iris encoder 226 is arranged to detect a relation between the rotating position of a rotor and that of a stator with a Hall element disposed within the iris driving mechanism 224 which includes a motor, etc.
A CPU 232 presides over control of the camera, i.e., the image pickup apparatus. A camera signal processing circuit 228 performs various signal processing actions such as amplifying and gamma correcting actions on a video signal, etc., outputted from the solid-state image sensor 221. A contrast signal (Y) included in the video signal thus processed is allowed to pass through an AE gate 229 and an AF gate 230. These gates 229 and 230 are arranged to set optimum signal take-out ranges within a whole image plane for deciding an exposure and focusing. In some cases, the take-out ranges are variable in size or are provided at a plurality portions of the image plane.
An AF signal processing circuit 231 is arranged to process an AF signal for AF (automatic focusing or focus adjustment). The AF signal processing circuit 231 forms one or a plurality of outputs relative to a high-frequency component of the video signal. The camera is provided with a zoom switch 233 and a zoom tracking memory 234. The zoom tracking memory 234 is arranged to store positions of the focusing lens unit 201d to be set according to object distances and positions of the variator lens unit 201b in performing a magnification varying action. A memory disposed within the CPU 232 may be used as the zoom tracking memory 234.
When the zoom switch 233 is operated by a user of the camera, the CPU 232 performs control in such a way as to keep the position of the variator lens unit 201b and that of the focusing lens unit 201d in a predetermined relation computed on the basis of information obtained from the zoom tracking memory 234. For this purpose, the zoom driving mechanism 222 and the focusing driving mechanism 223 are driven and controlled in such a way as to cause the current absolute position of the variator lens unit 201b in the direction of the optical axis as detected by the zoom encoder 225 to coincide with a computed position where the variator lens unit 201b is to be set, and-to cause the current absolute position of the focusing lens unit 201d in the direction of the optical axis as detected by the focus encoder 227 to coincide with a computed position where the focusing lens unit 201d is to be set.
In performing an automatic focusing (AF) action, the CPU 232 controls the focusing driving mechanism 223 in such a way as to cause the output of the AF signal processing circuit 231 to show a peak value.
Further, to obtain an apposite exposure, the CPU 232 controls the aperture diameter of the iris device 235 through the iris driving mechanism 224 in such a way as to cause the output of the iris encoder 226 to become a predetermined value with the average value of a Y signal output passing through the AE gate 229 set at the predetermined value.
During recent years, a reduction in size and diameter of photo-taking lenses has come to be desired. However, in this respect, a zoom lens of the optical type having four lens units arranged in the order of a fixed convex lens unit, a movable concave lens unit, a fixed convex lens unit and a movable convex lens unit, from the side of the object of shooting, has presented such a problem that the total length of a lens barrel holding the optical system inevitably becomes long, because the front lens unit is arranged to be stationary.
To solve this problem, therefore, a drawn-in (stowing) type lens barrel has been developed to draw in the front lens unit toward a camera body in stowing the lens barrel. For the same purpose, a front-lens-position-variable type zoom lens also has been developed to shorten the total length of the optical system at a wide-angle end position.
However, since a helicoid is used for the lens barrel structure of the draw-in type or the front-lens-position-variable type, these lens barrel structures become complex and large in size. In addition to this drawback, they increase the number of necessary parts to cause an increase in cost.
Further, in a case where the helicoid is not used, a driving action is performed with rack members formed at a lead screw and moving lens units. In that case, however, if an external force happens to be exerted on the front lens unit, the position of the front lens unit would come to deviate from a normal position to cause the so-called rack deviation. The rack deviation ruins information on the position of the front lens unit. Under such a condition, the control for maintaining an in-focus state by keeping the front lens unit and the focusing lens unit at desired distances from each other over the whole range of focal lengths becomes no longer possible. In order to recover the normal state of control, an action of verifying the initial positions of the front lens unit and the focusing lens unit must be first performed by restarting a power supply.
It is an object of the invention to provide an optical apparatus, such as a lens barrel, which is capable of driving a moving unit to move within a usage area and also to a stowed position with a simple cam mechanism.
It is another object of the invention to provide a compact optical apparatus which is capable of preventing any rack deviation even in a case where an external force happens to be exerted on the front lens unit (leading lens unit) and is capable of securing an in-focus state after removal of such an external force.
To attain the above objects, in accordance with one aspect of the invention, there is provided an optical apparatus, which comprises a first unit holding member and a second unit holding member arranged to hold a first optical unit and a second optical unit, respectively, a driven member arranged to be driven to move in an optical axis direction, and a cam member of a plate-like shape having a cam part, the cam member being capable of taking a first state in which the cam member rotates around a predetermined axis, without moving in the optical axis direction, according to movement of the driven member in the optical axis direction, and a second state, different from the first state, in which the cam member moves in the optical axis direction according to movement of the driven member in the optical axis direction, wherein, when taking each of the first state and the second state, the cam member drives the first unit holding member and the second unit holding member in the optical axis direction.
The optical apparatus further comprises a first guide member arranged to guide the first unit holding member in the optical axis direction, a first urging member arranged to urge the first unit holding member to move toward an object side, a second guide member arranged to guide the second unit holding member in the optical axis direction, and a second urging member arranged to urge the second unit holding member to move toward the object side.
Then, the cam member is a cam lever having a first end surface cam part and a second end surface cam part. The first unit holding member engages the first end surface cam part against an urging force of the first urging member. The second unit holding member engages the second end surface cam part against an urging force of the second urging member.
The cam member is provided with a long slot and a curved slot which branches from the long slot, and at least one of two pin members extending from a fixed member is fitted into the long slot.
In a state where the other of the two pin members is also fitted into the long slot, the cam member moves in the optical axis direction along the long slot, and, in a state where the other of the two pin members is fitted into the curved slot, the cam member rotates.
Further, in the state where the other of the two pin members is fitted into the curved slot, the cam member rotates to drive the first unit holding member and the second unit holding member in the optical axis direction so as to effect a zooming function.
Further, in the state where the other of the two pin members is also fitted into the long slot, the cam member moves in the optical axis direction along the long slot to cause the first unit holding member and the second unit holding member to move in the optical axis direction in such a way as to bring the optical apparatus into a standby state for a photo-taking operation.
The driven member and the first unit holding member move integrally with each other in the optical axis direction, and the cam member is pivotally supported by the first unit holding member.
In the optical apparatus, the cam member is provided with a first long slot, and a pin provided on the second unit holding member is fitted into the first long slot.
The cam member is further provided with a second long slot, and a pin provided on a fixed member is fitted into the second long slot.
The second long slot has two rectilinear portions.
The first unit holding member holds a lens unit located at a position closest to an object side.
The optical apparatus is a lens barrel.
In accordance with another aspect of the invention, there is provided an optical apparatus, which comprises a first unit holding member and a second unit holding member arranged to hold a first optical unit and a second optical unit, respectively, a first guide member arranged to guide the first unit holding member in an optical axis direction, a second guide member arranged to guide the second unit holding member in the optical axis direction, an urging member arranged to urge the first unit holding member to move toward an object side, and a cam member of a plate-like shape having a first cam part formed as an end surface cam and a second cam part, the cam member being arranged to rotate around a predetermined axis, wherein the end surface cam of the first cam part engages the first unit holding member against an urging force of the urging member, and the second cam part engages the second unit holding member, and wherein the first unit holding member and the second unit holding member move in the optical axis direction according to rotation of the cam member.
In the optical apparatus, the second cam part is a long slot, the long slot engaging a pin provided on the second unit holding member.
The optical apparatus further comprises a driving unit arranged to drive the second unit holding member in the optical axis direction.
In the optical apparatus, the driving unit includes an axial member which longitudinally extends in the optical axis direction and is provided with a helical groove, and a motor member arranged to drive the axial member to rotate, and the second unit holding member is driven in the optical axis direction along the helical groove according to the axial member being rotated.
In the optical apparatus, the first optical unit is a lens unit located at a position closest to the object side.
These and other objects and features of the invention will become apparent from the following detailed description of preferred embodiments thereof taken in connection with the accompanying drawings.